Catheters are widely used to reach a desired site within the circulatory system of a patient, such the heart and adjacent arteries, to perform diagnostic or therapeutic medical procedures. Such catheters utilize a variety of designs to suit the requirements of specific medical procedures. In many cases, these catheters provide significant torsional rigidity while retaining sufficient longitudinal flexibility and stiffness. Accordingly, a wide array of devices address these needs, including various guidewires and steering spines.
For example, guidewires having variable stiffness along the length are known in the art, where the highest degree of flexibility is generally located at the distal end. Some past disclosures, such as U.S. Pat. Nos. 5,743,876 and 5,605,543 set forth guidewires and guidewire tubes with slots or perforations of uniform shape and dimension to provide flexibility. These references disclose axial spacing between the slots that varies along the length of a guidewire tube, with spacing closer at the distal end than at the proximal end. This arrangement made the guidewire more flexible at the distal end than at the proximal end. Other guidewire designs, such as U.S. Pat. No. 5,437,288 to Schwartz, use a pattern of grooves having increasing radial depth as the pattern approaches the distal tip, thus similarly providing a greater flexibility at the distal portion of the pattern than at the proximal portion of the pattern.
Steering spines represent another category of prior art catheter devices developed to provide certain flexibility and torsional characteristics. Steering spines are generally characterized by a continuous “spine” portion that extended the length of the steering mechanism. U.S. Pat. No. 5,685,868 to Lundquist describes an example of a steering spine. In some devices, this configuration was embodied by a slotted tube having a continuous spine portion along one side. Because the spine is the only continuous member that extended the length of the steering mechanism, it is the only member that can transmit torque. Some prior art devices, like the one described in U.S. Pat. No. 6,890,329 to Carroll et al, limit the minimum bend radius of the catheter as well.
Furthermore, a number of steering spines of variable stiffness and enhanced flexibility at the distal tip are found in the prior art. U.S. Pat. No. 6,776,765 to Soukup discloses a stylet wire having a lumen and a pull wire positioned within the lumen with the distal end portion of the pull wire secured to the stylet wire proximate the distal end portion of stylet wire. The stylet wire further includes notches that alter the strength of the wall of the stylet wire in the distal region. These notches allow the stylet wire to more easily bend when the relative tension force is applied between the stylet wire and the pull wire. In some embodiments, the radial depth of the notches are progressively increased from proximal to distal to accomplish the strength alteration.
Other steering spines of variable stiffness, such as disclosed in U.S. Pat. No. 5,507,725, include a strengthening member with diametrically opposed struts extending between ring structures. The struts can be tapered to achieve the desired flexing profile. Other steering spine designs, such as disclosed by U.S. Pat. No. 5,304,131 to Paskar, utilize a tube with crescent-shaped slots formed on one side. Paskar discloses the radial depth of the slots as increasing from proximal to distal along the axis of the steering spine, causing the tube to preferentially bend first at the gap with the greatest depth (i.e. the distal-most gap), and next at the gap with the second greatest depth, and finally at the gap with the least depth when tension is applied to the pull wire. The crescent shape enhances the torsional rigidity of the tube when the tube is bent so that the gaps are closed.
Other steering devices implement helically wound ribbons within a unitary structure to give the catheter torsional rigidity for turning and steering as the catheter is inserted, for example, into a biological lumen or other body passage. See U.S. Pat. No. 4,516,972 to Samson. The stiffness and torsional rigidity of the catheter can be varied along the length by varying the pitch of the helical wound ribbons. U.S. Pat. No. 3,802,440 to Salem, et al., discloses an introducer in which the extreme distal portion has a degree of curvature greater than that of the remainder of the distal portion. This result is achieved by increasing the depth and lateral length of the more distal slots in the tube member relative to the more proximal slots. Salem further discloses enhancement of the effect by varying the spacing between the slots. A combination of greater slot depth, greater slot length and closer slot spacing can be used to increase flexibility.
Segmented steering mechanisms are also known in the prior art. Segmented steering mechanisms are different from steering spine mechanisms in several ways. Unlike steering spine mechanisms, segmented steering mechanisms are not “unitary bodies” because there is no continuous portion that extends the length of the mechanism. Accordingly, while segmented steering mechanism can be formed from a unitary body, they are not unitary after formation, and thus lack the resiliency of a unitary body. Therefore, segmented steering mechanisms require additional structure to control bending, such as a second pull wire. Also, segmented steering mechanisms generally rely on structure between adjacent segments, such as the pivots, to translate torque. See U.S. Pat. No. 5,749,828 to Solomon et al. and U.S. Pat. No. 5,807,241 to Heimburger as examples of devices having segmented steering mechanisms.
Despite significant disclosures of catheter designs found in the prior art, new and improved designs continue to be desired which could provide improved flexibility and better accommodate the torque imposed during certain procedures.
It is therefore desired to provide a catheter apparatus with a deflectable tip section, such as a steering spine, that can accommodate significant torque, allow considerable flexibility, and provide an improved and more uniform bend radius along the length of the steering spine.